Dimeric compounds and their use as anti-viral agents

ABSTRACT

The invention relates to compounds of general formula (I); in which R is an amino or guanidino group; R 2  is acetyl or trifluoroacetyl; and n is an integer from 10 to 18 or a pharmaceutically acceptable derivative thereof, methods for their preparation, pharmaceutical formulations containing them or their use in the prevention or treatment of a viral infection.

This invention relates to new chemical compounds and their use in medicine. In particular the invention concerns novel dimeric compounds, methods for their preparation, pharmaceutical formulations thereof and their use as anti-viral agents.

BACKGROUND OF THE INVENTION

Enzymes with the ability to cleave N-acetyl neuraminic acid (NANA), also known as sialic acid, from other carbohydrates are present in many microorganisms. These include bacteria such as Vibrio cholerae, Clostridium perfringens, Streptococcus pneumoniae and Arthrobacter sialophilus, and viruses such as influenza virus, parainfluenza virus, mumps virus, Newcastle disease virus and Sendai virus. Most of these viruses are of the orthomyxovirus or paramyxovirus groups, and carry a neuraminidase activity on the surface of the virus particles. Many of these neuraminidase-possessing organisms are major pathogens of man and/or animals, and some, such as influenza virus and Newcastle disease virus, cause diseases of enormous importance.

It has long been thought that inhibitors of neuraminidase might prevent infection by neuraminidase-bearing viruses. Most of the known neuraminidase inhibitors are analogues of neuraminic acid, such as 2-deoxy-2,3-dehydro-N-acetylneuraminic acid (DANA) and some of its derivatives (Meindl et al, Virology, 1974 58 457). Our International Patent Publication No. WO 91/16320 describes a number of analogues of DANA which are active against viral neuraminidase, and it has been shown in particular that 4-guanidino-2-deoxy-2,3-dehydro-N-acetylneuraminic acid (Compound (A), code number GG167) is useful in the treatment of influenza A and B (N. Engl. J. Med., 1997 337 874-880). Other patent applications describe various closely-related sialic acid derivatives (eg. PCT Publications No. WO 95/18800, No. WO 95/20583 and No. WO 98/06712), and anti-viral macromolecular conjugates of GG167 have also been described (International Patent Application No. PCT/AU97/00771).

International Patent Publication No. WO 00/55149, describes dimeric compounds which comprise two neuraminidase binding molecules, such as compound (A), attached to a common spacer or linking group of up to 100 atoms in length.

We have now discovered a novel class of compounds which fall within the generic scope of International Patent Publication No. WO 00/55149, but which are not specifically disclosed therein, and exhibit a surprisingly advantageous anti-influenza activity profile which includes an enhanced lung residency time and high potency.

Without wishing to be bound by theory, the basis for the long residency time in the lungs is thought to be due to the size and molecular weight of the compounds preventing entry through tight junctions in the respiratory epithelium and the polarity of the compounds being such that passage through the cell membranes occurs very inefficiently. An alternative theory is that the compounds themselves interact with the phospholipids in the cell membrane or other components of the respiratory epithelium and increase the residency time in the lungs.

SUMMARY OF THE INVENTION

In a first aspect, the present invention provides for a compound of general formula (I):

in which

R is an amino or guanidino group;

R² is acetyl or trifluoroacetyl; and

n is an integer from 10 to 18

or a pharmaceutically acceptable derivative thereof.

Preferably R is a guanidino group.

Preferably R² is an acetyl group.

Preferably n is 10 to 14, most preferably 12 to 14.

It will be appreciated by those skilled in the art that the compounds of formula (I) may be modified to provide pharmaceutically acceptable derivatives thereof at any one or more of the functional groups in the compounds of formula (I). Of particular interest as such derivatives are compounds modified at the carboxyl function, hydroxyl functions or at amino groups. Thus compounds of interest include alkyl esters, such as methyl, ethyl, propyl or isopropyl esters, aryl esters, such as phenyl, benzoyl esters, and acetyl esters of the compounds of formula (I).

The term “pharmaceutically acceptable derivative” means any pharmaceutically acceptable salt, ether, ester or salt of such ester of a compound of formula (I) or any other compound which, upon administration to the recipient, is capable of providing a compound of formula (I) or an anti-virally active metabolite or residue thereof. Of particular interest as derivatives are compounds modified at the sialic acid carboxy or glycerol hydroxy groups, or at amino and guanidine groups.

Pharmaceutically acceptable salts of the compounds of formula (I) include those derived from pharmaceutically acceptable inorganic and organic acids and bases. Examples of suitable acids include hydrochloric, hydrobromic, sulphuric, nitric, perchloric, fumaric, maleic, phosphoric, glycollic, lactic, salicylic, succinic, toluene-p-sulphonic, tartaric, acetic, citric, methanesulphonic, formic, benzoic, malonic, naphthalene-2-sulphonic and benzenesulphonic acids. Other acids such as oxalic acid, while not in themselves pharmaceutically acceptable, may be useful in the preparation of salts useful as intermediates in obtaining compounds of the invention and their pharmaceutically acceptable acid addition salts.

Salts derived from appropriate bases include alkali metal (eg. sodium), alkaline earth metal (eg. magnesium), ammonium, and NR₄ ⁺ (where R is C₁₋₄alkyl) salts.

The compounds of the invention may be prepared by methods described herein. It will be apparent to those skilled in the art, that it is necessary to use protecting groups to protect one or more functional groups of the neuraminidase binding molecule during the process of attaching the monomers to the alkyl spacer group. See for example “Protective Groups in Organic Synthesis” by T. W. Green and P. G. M. Nuts (John Wiley & Sons, 1991). Pharmaceutically acceptable salts of the compounds of formula (I) may be prepared according to known procedures.

Accordingly, the present invention also provides a method for the preparation of the compound of formula (I), which comprises the step of deprotection of a compound of formula (II)

in which n is as defined above, P₁ is a carboxylic acid protecting group and P₂ is an amine protecting group.

The present invention further provides a method for the preparation of the compound of formula (I), which comprises the steps of:

(a) reacting a compound of formula (III)

in which P₁ and P₂ are as defined above,

with a compound of formula (IV): OCN(CH₂)_(n)NCO  (IV)

in which n is as defined above to form the compound of formula (II) as defined above; and

(b) deprotection of the compound of formula (II).

The present invention still further provides a method for the preparation of the compound of formula (I) which comprises the steps of:

(a) protecting a compound of formula (V)

in which P₁ and P₂ are as defined above

to form the compound of formula (III) as defined above;

(b) reacting the compound of formula (III) with the compound of formula (IV) as defined above to form the compound of formula (II) as defined above; and

(c) deprotection of the compound of formula (II).

For use in therapy it is preferable that the compounds of formula (I) are in crystalline form. We have found that the compound of formula (I) in which R is a guanidino group, R² is an acetyl group and n is 13 (Example 4 below) can be prepared in crystalline form by crystallisation from aqueous solution by procedures described herein.

The compounds of formula (I) possess antiviral activity. In particular these compounds are inhibitors of viral neuraminidase of orthomyxoviruses and paramyxoviruses, for example the viral neuraminidase of influenza A and B, parainfluenza, mumps and Newcastle disease.

Thus in a second aspect the invention provides a compound of formula (I) or a pharmaceutically acceptable derivative thereof, for use as an active therapeutic agent in the treatment of a viral infection, for example orthomyxovirus and paramyxovirus infections.

In a third aspect the invention provides a method for the prevention or treatment of a viral infection comprising the step of administration to a subject in need thereof of an effective amount of a compound of formula (I), or a pharmaceutically acceptable salt or derivative thereof.

Preferably, the viral infection is an orthomyxovirus or paramyxovirus infection. More preferably the viral infection is an influenza A or B infection.

Preferably the subject is an animal such as a mammal, more preferably a human, or a member of the genus Equus, for example a horse, donkey or mule. Most preferably the mammal is a human.

In a fourth aspect the invention provides use of a compound of the invention for the manufacture of a medicament for the treatment of a viral infection.

As used herein, the term “effective amount” is meant an amount of the compound of formula I effective to preventing or treating a viral infection in order to yield a desired therapeutic response. For example, to overcome or alleviate the effects of a viral infection.

The term “therapeutically-effective amount” means an amount of the compound of formula I to yield a desired therapeutic response. For example, treating or preventing a viral infection.

The specific “therapeutically-effective amount” will, obviously, vary with such factors as the particular viral infection being treated, the physical condition of the subject, the type of animal being treated, the duration of the treatment, the nature of concurrent therapy (if any), and the specific formulation employed and the structure of the compound or its derivatives.

Generally, the terms “treating”, “treatment” and the like are used herein to mean affecting a subject, tissue or cell to obtain a desired pharmacologic and/or physiologic effect. The effect may be prophylactic in terms of completely or partially preventing a viral infection or sign or symptom thereof, and/or may be therapeutic in terms of a partial or complete cure of a viral infection. “Treating” as used herein covers any treatment of, or prevention of a viral infection in a vertebrate, a mammal, particularly a human, and includes: (a) preventing the viral infection from occurring in a subject that may be predisposed to the viral infection, but has not yet been diagnosed to the viral infection, but has not yet been diagnosed as having it; (b) inhibiting the viral infection, ie., arresting its development; or (c) relieving or ameliorating the effects, i.e., cause regression of the symptoms of the viral infection.

The compounds of the invention may also be used in diagnostic methods, in particular methods for the detection of influenza virus. For use in such methods it may be advantageous to link a compound of the invention to a label, such as a radioactive, fluorescent or chemiluminescent label.

Methods of diagnosis for which the compounds of the invention are suitable are described, for example, in our earlier applications PCT/AU97/00109 and PCT/AU97/00771.

In a fifth aspect the invention provides a method for the detection of a viral infection which comprises the step of contacting the compound of the invention with a sample suspected of containing the virus.

It will be further appreciated that the amount of a compound of the invention required for use in treatment will vary not only with the particular compound selected but also with the route of administration, the nature of the condition being treated, and the age and condition of the patient, and will ultimately be at the discretion of the attendant physician or veterinarian. In general however, a suitable dose will be in the range of from about 0.001 to 100 mg/kg of bodyweight per day, preferably in the range of 0.01 to 10 mg/kg/day, most preferably in the range of 0.1 to 1 mg/kg/day.

Treatment is preferably commenced before or at the time of infection and continued until virus is no longer present in the respiratory tract. However the compounds are also effective when given post-infection, for example after the appearance of established symptoms.

Suitably treatment is given on one or two occasions, preferably only once only for treatment, and preferably once per week for prophylaxis.

The compound is conveniently administered in unit dosage form, for example containing 1 to 100 mg, more conveniently 1 to 20 mg of active ingredient per unit dosage form.

While it is possible that, for use in therapy, a compound of the invention may be administered as the raw chemical, it is preferable to present the active ingredient as a pharmaceutical formulation.

Thus in a sixth aspect the invention provides a pharmaceutical formulation comprising a compound of formula (I) or a pharmaceutically acceptable salt or derivative thereof, together with one or more pharmaceutically acceptable carriers therefor and, optionally, other therapeutic and/or prophylactic ingredients. The carrier(s) must be “acceptable” in the sense of being compatible with the other ingredients of the formulation and not being deleterious to the recipient thereof.

The compounds of the invention may also be used in combination with other therapeutic and/or prophylactic agents, for example other anti-infective agents. In particular the compounds of the invention may be employed with other antiviral agents. The invention thus provides in a seventh aspect a combination comprising a compound of formula (I) or a pharmaceutically acceptable salt or derivative thereof together with another therapeutically and/or prophylactically active agent, in particular an antiviral agent.

The combinations referred to above may conveniently be presented for use in the form of a pharmaceutical formulation and thus such formulations comprising a combination as defined above together with a pharmaceutically acceptable carrier therefor comprise a further aspect of the invention.

Suitable therapeutic and/or prophylactic agents for use in such combinations include other anti-infective agents, in particular anti-bacterial and anti-viral agents such as those used to treat respiratory infections. For example, other compounds or vaccines effective against influenza viruses, such as the sialic acid analogues referred to above, e.g. zanamivir, oseltamivir, amantadine, rimantadine and ribavirin and FluVax, may be included in such combinations.

The individual components of such combinations may be administered either separately, sequentially or simultaneously in separate or combined pharmaceutical formulations.

When the compounds of the invention are used with a second therapeutic and/or prophylactic agent active against the same virus, the dose of each compound may either be the same as or different from that employed when each compound is used alone. Appropriate doses will be readily appreciated by those skilled in the art.

Pharmaceutical formulations include those suitable for oral, rectal, nasal, topical (including buccal and sub-lingual), vaginal or parenteral (including intramuscular, sub-cutaneous and intravenous) administration, or those in a form suitable for administration to the respiratory tract (including the nasal passages) for example by inhalation or insufflation. The formulations may, where appropriate, be conveniently presented in discrete dosage units, and may be prepared by any of the methods well known in the art of pharmacy. These methods include the step of bringing into association the active compound with liquid carriers or finely divided solid carriers or both, and then, if necessary, shaping the product into the desired formulation.

Pharmaceutical formulations suitable for oral administration may conveniently be presented as discrete units such as capsules, cachets or tablets each containing a predetermined amount of the active ingredient; as a powder or granules; as a solution, a suspension or as an emulsion. The active ingredient may also be presented as a bolus, electuary or paste. Tablets and capsules for oral administration may contain conventional excipients such as binding agents, fillers, lubricants, disintegrants, or wetting agents. The tablets may be coated according to methods well known in the art. Oral liquid preparations may for example be in the form of aqueous or oily suspensions, solutions, emulsions, syrups or elixirs, or may be presented as a dry product for constitution with water or other suitable vehicle before use. Such liquid preparations may contain conventional additives such as suspending agents, emulsifying agents, non-aqueous vehicles, which may include edible oils, or preservatives.

The compounds according to the invention may also be formulated for parenteral administration by injection, for example bolus injection, or continuous infusion, and may be presented in unit dose form in ampoules, pre-filled syringes, small volume infusion or in multi-dose containers with an added preservative. The compositions may take such forms as suspensions, solutions, or emulsions in oily or aqueous vehicles, and may contain formulating agents such as suspending, stabilising and/or dispersing agents. Alternatively, the active ingredient may be in powder form, obtained by aseptic isolation of sterile solid or by lyophilisation from solution, for constitution with a suitable vehicle, eg. sterile, pyrogen-free water, before use.

For topical administration to the epidermis the compounds according to the invention may be formulated as ointments, creams or lotions, or as a transdermal patch. Ointments and creams may, for example, be formulated with an aqueous or oily base with the addition of suitable thickening and/or gelling agents. Lotions may be formulated with an aqueous or oily base, and will in general also contain one or more emulsifying agents, stabilising agents, dispersing agents, suspending agents, thickening agents, or colouring agents.

Formulations suitable for topical administration in the mouth include lozenges comprising active ingredient in a flavoured base, usually sucrose and gum acacia or gum tragacanth; pastilles comprising the active ingredient in an inert base such as gelatin or sucrose and gum acacia; and mouthwashes comprising the active ingredient in a suitable liquid carrier.

Pharmaceutical formulations suitable for rectal administration wherein the carrier is a solid are most preferably presented as unit dose suppositories. Suitable carriers include cocoa butter and other materials commonly used in the art, and the suppositories may be conveniently formed by admixture of the active compound with the softened or melted carrier(s) followed by chilling and shaping moulds.

Formulations suitable for vaginal administration may be presented as pessaries, tampons, creams, gels, pastes, foams or sprays containing in addition to the active ingredient such carriers as are known in the art to be appropriate.

For administration to the respiratory tract, including intranasal administration, the neuraminidase inhibitors may be administered by any of the methods and formulations employed in the art for administration to the respiratory tract.

Thus in general the compounds may be administered in the form of a solution or a suspension or as a dry powder.

Solutions and suspensions will generally be aqueous, for example prepared from water alone (for example sterile or pyrogen-free water) or water and a physiologically acceptable co-solvent (for example ethanol, propylene glycol or polyethylene glycols such as PEG 400).

Such solutions or suspensions may additionally contain other excipients for example preservatives (such as benzalkonium chloride), solubilising agents/surfactants such as polysorbates (eg. Tween 80, Span 80, benzalkonium chloride), buffering agents, isotonicity-adjusting agents (for example sodium chloride), absorption enhancers and viscosity enhancers. Suspensions may additionally contain suspending agents (for example microcrystalline cellulose, carboxymethyl cellulose sodium).

Solutions or suspensions are applied directly to the nasal cavity by conventional means, for example with a dropper, pipette or spray. The formulations may be provided in single or multidose form. In the latter case a means of dose metering is desirably provided. In the case of a dropper or pipette this may be achieved by the patient administering an appropriate, predetermined volume of the solution or suspension. In the case of a spray this may be achieved for example by means of a metering atomising spray pump.

Administration to the respiratory tract may also be achieved by means of an aerosol formulation in which the compound is provided in a pressurised pack with a suitable propellant, such as a chlorofluorocarbon (CFC), for example dichlorodifluoromethane, trichlorofluoromethane or dichlorotetrafluoroethane, carbon dioxide or other suitable gas. The aerosol may conveniently also contain a surfactant such as lecithin. The dose of drug may be controlled by provision of a metered valve.

Alternatively the compounds may be provided in the form of a dry powder, for example a powder mix of the compound in a suitable powder base such as lactose, starch, starch derivatives such as hydroxypropylmethyl cellulose and polyvinylpyrrolidine (PVP). Conveniently the powder carrier will form a gel in the nasal cavity. The powder composition may be presented in unit dose form, for example in capsules or cartridges of eg. gelatin, or blister packs from which the powder may be administered by means of an inhaler.

In formulations intended for administration to the respiratory tract, including intranasal formulations, the compound will generally have a small particle size, for example of the order of 5 microns or less. Such a particle size may be obtained by means known in the art, for example by micronisation.

When desired, formulations adapted to give sustained release of the active ingredient may be employed.

Preferably the compounds of the invention are administered to the respiratory tract by inhalation, insufflation or intranasal administration, or a combination thereof.

“Relenza” is administered by oral inhalation as a free-flow powder via a “Diskhaler” (trade marks of the GlaxoSmithKline group of companies). A similar formulation would be suitable for the present invention.

Thus, according to an eighth aspect of the present invention there is provided an inhaler which contains a formulation as defined above.

It will be appreciated that the inhaler may also be in the form of a meter dose aerosol inhaler.

For the purposes of this specification it will be clearly understood that the word “comprising” means “including but not limited to”, and that the word “comprises” has a corresponding meaning.

All publications, including but not limited to patents and patent applications, cited in this specification are herein incorporated by reference as if each individual publication were specifically and individually indicated to be incorporated by reference herein as though fully set forth.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described in detail by way of reference only to the following non-limiting examples.

Machine Methods

Method A (LC/MS)

Micromass Platform II mass spectrometer operating in positive ion electrospray mode, mass range 100-1000 amu.

Column: 3.3 cm×4.6 mm ID, 3 μm ABZ+PLUS

Flow Rate: 3 ml/min

Injection Volume: 5 μl

Solvent A: 95% acetonitrile+0.05% formic acid

Solvent B: 0.1% formic acid+10 mMolar ammonium acetate

Gradient: 0-100% A/5 min, 100-0% B/5 min

Method B

The prep column used was a Supelcosil ABZplus (10 cm×2.12 cm).

UV wavelength: 230 nm

Flow: 4 ml/min

Solvent A: acetonitrile+0.05% TFA

Solvent B: water+0.1% TFA

Gradient: 20-40% A/20 min, 40% A/20 min, 40-100% A/0.3 min, 100% A/15 min, 100-20% A/3 min

Abbreviations

TFA trifluoroacetic acid

DMAP 4-dimethylaminopyridine

SPE solid phase extraction

DPM diphenylmethane

BOC t-butoxycarbonyl group

Preparation of Intermediate 1

Benzhydryl (2R,3R,4S)-3-(acetylamino)-4-({(E)-[(tert-butoxycarbonyl)amino][(tert-butoxycarbonyl)imino]methyl}amino)-2-[(1R,2R)-1,2,3-trihydroxypropyl]-3,4-dihydro-2H-pyran-6-carboxylate (see J. Med. Chem. 1998, 41, 787-797) (12.38 g; 17.7 mmoles) was dissolved in dry acetonitrile (130 ml) under nitrogen at room temperature. The solution was stirred and 1,1′-carbonyldiimidazole (2.87 g; 17.7 mmoles) was added. After 16 hours LC/MS showed the presence of starting triol so further 1,1′-carbonyldiimidazole (total of 0.493 g; 3 mmoles) was added. After a few hours LC/MS showed no triol present. The solvent was evaporated and the residue flash columned on silica, eluting with 1:1 ethyl acetate/40-60 petroleum ether. Fractions containing wanted product were evaporated then taken up in dichloromethane, dried with sodium sulphate, filtered and evaporated to give Intermediate 1 (benzhydryl (2R,3R,4S)-3-(acetylamino)-4-({[(tert-butoxycarbonyl)amino][(tert-butoxycarbonyl)imino]methyl}amino)-2-{(S)-hydroxy[(4R)-2-oxo-1,3-dioxolan-4-yl]methyl}-3,4-dihydro-2H-pyran-6-carboxylate) as an off white solid (11.05 g; 86%). Preparation of Intermediate 10

Intermediate 1 (0.4 g; 0.56 mmole) was dissolved in dry dichloromethane (0.5 ml). To this was added DMAP (20 mg) and 4 molecular sieves type 3A followed by intermediate 5 (50 mg, 0.19 mmole). The mixture was refluxed overnight then applied directly to a 10 g Si SPE cartridge eluted with diethyl ether and ethyl acetate to give intermediate 10 as a colourless glass (0.16 g, 50% yield).

LC/MS (method A) showed (M+2H⁺)/2=858; T_(RET)=4.68 min.

Similarly prepared were the following: n diisocyanate dicarbamate (M + 2H⁺)/2 T_(RET)(min) 10 intermediate 2 intermediate 7 837 4.58 11 intermediate 3 intermediate 8 844 4.68 12 intermediate 4 intermediate 9 851 4.66 14 intermediate 6 intermediate 11 865 4.75 Preparation of Intermediate 15

Intermediate 10 (0.16 g; 0.093 mmole) was dissolved in a 10:1 mixture of dichloromethane:anisole (6.3 ml) at room temperature. To this was added TFA (6.3 ml) and the resulting solution was stirred for 2.5 hours then evaporated in vacuo. Trituration of the residue with ether gave intermediate 15 as the di-TFA salt (92 mg; 82% yield). LC/MS (method A) showed (M+2H⁺)/2=492; T=2.61 min.

Similarly prepared were the following: starting n material product (M + 2H⁺)/2 T_(RET)(min) 10 intermediate 7 intermediate 12 471 2.31 11 intermediate 8 intermediate 13 478 2.43 12 intermediate 9 intermediate 14 485 2.51 14 intermediate 11 intermediate 16 499 2.68

EXAMPLE 4 n=13 (2R,3R,4S)-3-(acetylamino)-2-{(1R,21R,22R)-21-((2R,3R,4S)-3-(acetylamino)-4-([amino(imino)methyl]amino}-6-carboxy-3,4-dihydro-2H-pyran-2-yl)-1-[(1R)-1,2-dihydroxyethyl]-22,23-dihydroxy-3,19-dioxo-2,20-dioxa-4,18-diazatricos-1-yl)-4-[({amino(imino)methyl]amino}-3,4-dihydro-2H-pyran-6-carboxylic acid bis(trifluoroacetic acid salt)

Intermediate 15 (92 mg; 0.076 mmole) was dissolved in a mixture of water (16 ml) and methanol (16 ml). To this was added triethylamine (4 ml) and the solution was stirred for 1 hour. Volatile organics were removed in vacuo and the residue adjusted to pH 2 with TFA. Reverse phase preparative HPLC (method B) gave example 4 as the di-TFA salt (35.5 mg; 40% yield). LC/MS (method A) showed (M+2H⁺)/2=466; T_(RET)=2.45 min.

Elemental analysis:—Found: C, 42.00; H, 5.79; N, 11.00%. Calc for tetrahydrate: C, 41.95; H, 6.18; N, 11.38%.

NMR (D₂O) δ: 5.85(2H,d,2×CH); 4.85(2H,dd,2×CH); 4.46(2H,dd,2×CH); 4.34(2H,dd,2×CH); 4.05,2H,t,2×CH); 3.94(2H,m,2×CH); 3.58(2H,d d, CH₂); 3.42 (2H,dd, CH₂); 2.95(4H,m,2×CH₂); 1.88 (6H, s,2×CH₃); 1.38(4H, br.m,2×CH₂); 1.22-1.10(18H,br.m,9×CH₂) p.p.m.

EXAMPLE 4a Large Scale Preparation of Example 4

Intermediate 15 (2.8 g; 2.3 mmoles) was dissolved in water (50.4 ml). To this was added methanol (50.4 ml) followed by triethylamine (6.4 ml; 46 mmoles). The resulting solution was stirred at room temperature for 5 hours, the volume of the reaction mixture was reduced by ca 33% in vacuo at 35 degrees C. then the pH was adjusted to 2 with TFA (0.5 ml). The acidified solution was then injected onto a Prochom LC50 HPLC system comprising of a 20 cm×5 cm column packed with 7 micron Kromasil C8 packing material. The column was subjected to gradient elution:

Solvent A: water+1% TFA

Solvent B: 75% acetonitrile/water+1% TFA

Flow: 80 ml/min

Gradient: 0% B to 100% B/40 min

The appropriate fractions were combined and the acetonitrile was removed in vacuo at 35 degrees C. The aqueous residue was absorbed onto a 10 cm×22 mm column of Amberchrom CG-161 (PSDVB resin) and the column washed with water then eluted with acetonitrile:MeOH:water 2:2:1 (500 ml). The solvent was removed in vacuo to yield a gum. The addition of isopropanol (20 ml) gave a solid which was dried to give the product as the zwitterion (1.68 g).

EXAMPLE 4b Crystallisation of Example 4

The zwitterion (100 mg; 0.1075 mmoles) was dissolved in water (35 ml). To this was added sodium bicarbonate (18.06 mg; 0.215 mmoles) and the resulting solution was freeze-dried to give a white solid. A sample (2 mg) of this solid was dissolved in water (0.8 ml) and evaporated to a syrupy oil. Dioxan (1 ml) was added and a white solid formed. The solid was allowed to settle and the supernatent was removed. Further dioxan (1 ml) was added and the supernatant was again removed. This process was repeated twice more and the solid obtained was dried in vacuo. Examination under polarised light showed crystallinity.

Examples E1, E2, E3 and E5 were prepared using an analogous procedure to that of Example E4.

EXAMPLE 1 n=10 (2R,3R,4S)-3-(acetylamino)-2-{(1R,18R,19R)-18-((2R,3R,4S)-3-(acetylamino)-4-{[amino(imino)methyl]amino}-6-carboxy-3,4-dihydro-2H-pyran-2-yl)-1-[(1R)-1,2-dihydroxyethyl]-19,20-dihydroxy-3,16-dioxo-2,17-dioxa-4,15-diazaicos-1-yl}-4-{[amino(imino)methyl]-amino}-3,4-dihydro-2H-pyran-6-carboxylic acid bis(trifluoroacetic acid salt)

LC/MS (method A) showed (M+2H⁺)/2=445; T_(RET)=2.13 min.

EXAMPLE 2 n=11 (2R,3R,4S)-3-(acetylamino)-2-{(1R,19R,20R)-19-((2R,3R,4S)-3-(acetylamino)-4-{[amino(imino)methyl]amino}-6-carboxy-3,4-dihydro-2H-pyran-2-yl)-1-[(1R)-1,2-dihydroxyethyl]-20,21-dihydroxy-3,17-dioxo-2,18-dioxa-4,16-diazahenicos-1-yl}-4-{[amino(imino)methyl]amino}-3,4-dihydro-2H-pyran-6-carboxylic acid bis(trifluoroacetic acid salt)

LC/MS (method A) showed (M+2H⁺)/2=452; T_(RET)=2.25 min.

EXAMPLE 3 n=12 (2R,3R,4S)-3-(acetylamino)-2-{(1R,20R,21R)-20-((2R,3R,4S)-3-(acetylamino)-4-{[amino(imino)methyl]amino}-6-carboxy-3,4-dihydro-2H-pyran-2-yl)-1-[(1R)-1,2-dihydroxyethyl]-21,22-dihydroxy-3,18-dioxo-2,19-dioxa-4,17-diazadocos-1-yl}-4-{[amino(imino)methyl]amino}-3,4-dihydro-2H-pyran-6-carboxylic acid bis(trifluoroacetic acid salt)

LC/MS (method A) showed (M+2H⁺)/2=459; T_(RET)=2.34 min.

EXAMPLE 5 n=14 (2R,3R,4S)-3-(acetylamino)-2-{(1R,22R,23R)-22-((2R,3R,4S)-3-(acetylamino)-4-{[amino(imino)methyl]amino}-6-carboxy-3,4-dihydro-2H-pyran-2-yl)-1-[(1R)-1,2-dihydroxyethyl]-23,24-dihydroxy-3,20-dioxo-2,21-dioxa-4,19-diazatetracos-1-yl}-4-{[amino(imino)methyl]amino}-3,4-dihydro-2H-pyran-6-carboxylic acid bis(trifluoroacetic acid salt)

LC/MS (method A) showed (M+2H⁺)/2=473; T_(RET)=2.50 min.

EXAMPLE 6 Evaluation of the Compounds of Formula (I)—Inhibition of Influenza Virus Replication

Cytopathic effect (CPE) assays were performed essentially as described by Watanabe et al. (J. Virological Methods, 1994 48 257). MDCK cells were infected with a defined inoculum of virus (determined by experimentation to be the minimum sufficient to cause adequate CPE in 72 hours and to be susceptible to control compounds at concentrations considered to be consistent with published norms) in the presence serial dilutions of Compounds of the invention. Cultures were incubated for up to 72 hours at 37° C. in a 5% CO₂ atmosphere. The extent of CPE and hence viral replication was determined via metabolism of the viral dye 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) according to published methods (see for example, Watanabe et al., 1994). The compound concentration that inhibited CPE by 50% (ID₅₀) was calculated using a computer program for curve fitting. Influenza A/Sydney/5/97 and B/Harbin/7/95 viruses were assayed and the results are shown in Table 1. Comparable data for a specifically disclosed compound in WO 00/55149 and for compound A is also shown in Table 1. TABLE 1 ID₅₀ μg/ml ID₅₀ M ID₅₀ μg/ml ID₅₀ M Description A/Sydney/5/97+ A/Sydney/5/97+ B/Harbin/7/95 B/Harbin/7/95 Compound A 0.023 +/− 0.024 69 0.013 +/− 0.011 39 E1 0.0002 0.179 0.0001 0.09 E2 0.0001 0.09 0.0001 0.09 E3 0.0001, 0.0001 0.087 0.0001, 0.0001 0.087 E4 0.0001 0.086 0.0001 0.086 E5 0.0001 0.085 0.0003 0.26 Compound 0.0007, 0.0005 0.58, 0.75 0.007 +/− 0.01 5.8 Number 8* Compound 0.057  66 >0.1 >115 Number 10* *As referenced in WO 00/55149 +Data provided in WO 00/55149 related to the virus H3N2 isolate A/Victoria/3/75 rather than A H3N2 isolate A/Sydney/5/97. When comparing such data the person skilled in the art will appreciate that differences in antiviral potency are not uncommon for a given compound when analysed against several different viruses in vitro. For example, Woods et al (Antimicrob Agents Chemother 1993 37: 1473-9) have reported that Compound A exhibits a wide range of EC50 # values (from 0.02 to 0.16 uM) in in vitro assays involving recent clinical isolates. Accordingly, compound 8 was found to be more potent in CPE assays involving the recent influenza A H3N2 isolate A/Sydney/5/97 than the earlier H3N2 isolate A/Victoria/3 /75.

Data provided in Table 1 demonstrate that the compounds E1-E5, in addition to being substantially more potent than the highly active compound A, are even more potent against A/Sydney/5/97 and substantially more potent against the recent influenza B isolate B/Harbin/7/95 than compounds 8 and 10 of WO 00/55149.

EXAMPLE 7 Plaque Reduction Assay

Madin Darby Canine Kidney (MDCK) cells are seeded into six well tissue culture plates and grown to confluency via standard methods. Influenza viruses are diluted in a minimal volume of phosphate buffered saline supplemented with 0.2% bovine serum albumin to yield an estimated titre of 50-100 plaque forming units (pfu) per well. After adsorption to the MDCK cells for one hour at 37° C. in a 5% CO₂ atmosphere the viral inocula is aspirated and replaced with viral growth media (minimal Eagle's media supplemented with BSA, trypsin and insulin/transferrin/selenium at optimal concentrations) containing sufficient agar or agarose (generally 1-2%) to cause the media to gel at room temperature and at 37° C. in a 5% CO₂ atmosphere until plaques develop (generally 2-4 days). Plaques can be visualised with a suitable stain (e.g. 0.4% crystal violet in formal saline) before counting. Antiviral potency is expressed as the concentration of test article which reduces plaque numbers by 50% of the untreated control value (EC₅₀). EC₅₀ ng/ml PRA Example A/WSN* A/Vic* A/Syd* A/New* A/Pan* A/Bay* Compound A 56, >100 5.5 +/− 8.2 2.4 0.27, 0.23 2.7, 3 35 3 0.0023 0.000429 2 0.06, 0.2 <0.0001 4 <0.0001 <0.001, <0.01, 0.2 <0.0001 0.043 <0.00001 5 <0.0001 <0.001, 0.02, 0.3 0.032 <0.0001 0.032 <0.0001 Amantadine 220 11 157 Oseltamivir 0.11 0.23 0.3 *A/WSN/33 BVLV09 (H1N1) A/Victoria/3/75 BVLV017 (H3N2) A/Sydney/5/97 BVLV015 (H3N2) A/New Caledonia/20/99 BVLV008 (H1N1) A/Panama/2007/99 BVLV008 (H3N2) A/Bayern/7/95 BVL006 (H1N1)

EC₅₀ ng/ml PRA Example B/Vic* B/Harb* B/HongK* B/Yam* Compound 3, 20 0.19 21 +/− 6 0.2, 3.1 A 3 0.009, 0.01 <0.0001 <0.0001, <0.0001 2 0.04, 0.05 <0.0001 4 0.01, 0.1 0.06 <0.0001 5 0.05, 0.1 0.37 <0.0001 Amantadine >10000 2061 Oseltamivir 32 0.7 *B/Victoria/1/67 B/Hong Kong/5/72 BVLV012 B/Harbin/7/95 BVLV008 B/Yamanashi/166/98 BVLV007

EXAMPLE 8 Assessment of Long Duration of Action

Rodents are anaesthetised and dosed with compound of interest by the intra-tracheal route at a dose volume of 0.8 ml/kg. The rodent is then held in the vertical position until full recovery is achieved. At different time points, for example, 2, 8, 24 and 48 hours post-dose, levels of compound in the lung tissue are assessed by analytical methods. Any analytical method suitable for detection of this type of compound may be used. The time at which levels of compound fall below the sensitivity of the analytical techniques identified will determine the residency time of the compound in lung tissue.

The rat lung retention data for selected compounds is shown below. Please note that all experiments included a co-dosed internal standard, namely compound 3 of International Patent Publication No. WO 02/20514, to permit comparison. The data are expressed as a ratio with respect to this compound, the structure of which is shown below.

The data for compound A is included for comparison purposes. The compounds of the invention have significantly greater retention at 7 days than Compound A when expressed as a ratio of compound concentration to standard concentration. Rat lung retention assay results time Mean PCT AU01/01128 Mean (PCT AU01/01128 Ratio Mean (lung) point dose (cmpd) (cmpd) compound 3 compound 3) (cmpd)/PCT hrs Compound mg/kg ng/g ng/g ng/g ng/g AU01/01128 compound 3 48 Example 3 0.1 591 1117 655 1413 0.79 48 Example 3 0.1 1845 1840 48 Example 3 0.1 914 1174 168 Example 3 0.1 111 376 242 550 0.68 168 Example 3 0.1 471 580 168 Example 3 0.1 546 829 48 Example 4 0.1 2414 1772 1098 1044 1.70 48 Example 4 0.1 1927 1352 48 Example 4 0.1 977 681 168 Example 4 0.1 929 756 636 509 1.48 168 Example 4 0.1 914 524 168 Example 4 0.1 426 367 48 Example 5 0.1 3044 4803 784 1478 3.25 48 Example 5 0.1 6268 2046 48 Example 5 0.1 5097 1605 168 Example 5 0.1 2750 1798 632 363 4.95 168 Example 5 0.1 1255 242 168 Example 5 0.1 1388 216 48 Compound A (zanamivir) 0.1 421 352 698 1368 0.26 48 Compound A (zanamivir) 0.1 369 1901 48 Compound A (zanamivir) 0.1 267 1507 168 Compound A (zanamivir) 0.1 91 61 815 750 0.08 168 Compound A (zanamivir) 0.1 47 925 168 Compound A (zanamivir) 0.1 45 512

EXAMPLE 9 Alternative Assessment of Long Duration of Action and Efficacy

The protocol for infecting mice has been described previously (1-4). Mildly anaesthetised mice are inoculated into the external nares with influenza virus. Treatment procedure and regimen. A single dose of compound is administered at a defined time point up to 10 days prior to infection, preferably 4-7 days prior to infection, or following infection, preferably immediately following infection and up to 48 hours post infection. In most experiments, a non-lethal strain of influenza is used, and efficacy is assessed by reductions in lung virus titre. For mice given compound prior to infection, lungs are removed post infection either on a single day, or on days following infection, preferably days 1-4 post infection. Homogenised lung samples are assayed for virus using established methods, and the titres of viral load estimated and compared to titres of virus in lungs of untreated mice.

In those experiments where a mouse-adapted lethal strain of influenza is used, efficacy is assessed by an increase in survival rate and/or numbers of survivors, as compared to untreated mice.

REFERENCES

-   1. Ryan, D. M., J. Ticehurst, M. H. Dempsey, and C. R. Penn, 1994.     Inhibition of influenza virus replication in mice by GG167     (4-guanidino-2,4-dideoxy-2,3-dehydro-N-acetylneuraminic acid) is     consistent with extracellular activity of viral neuraminidase     (sialidase). Antimicrob. Agents and Chemother. 38 (10):2270-2275. -   2. von Itzstein M., W.-Y. Wu, G. B. Kok, M. S. Pegg, J. C.     Dyason, B. Jin, T. V. Phan, M. L. Smythe, H. F. White, S. W.     Oliver, P. M. Colman, J. N. Varghese, D. M. Ryan, J. M. Woods, R. C.     Bethell, V. J. Hogham, J. M. Cameron, and C. R. Penn. 1993. Rational     design of potent sialidase-based inhibitors of influenza virus     replication. Nature (London) 363:418-423. -   3. Woods, J. M., R. C. Bethell, J. A. V. Coates, N. Healey, S. A.     Hiscox, B. A. Pearson, D. M. Ryan, J. Ticehurst, J. Tilling, S. A.     Walcott, and C. R. Penn. 1993.     4-Guanidino-2,4-dideoxy-2,3-dehydro-N-acetylneuraminic acid is a     highly effective inhibitor both of the sialidase (neuraminidase) and     of growth of a wide range of influenza A and B viruses in vitro.     Antimicrob. Agents Chemother. 37:1473-1479. -   4. Robert J Fenton, Peter J Morley, Ian J Owens, David Gower, Simon     Parry, Lee Crossman and Tony Wong (1999). Chemoprophylaxis of     influenza A virus infections, with single doses of zanamivir,     demonstrates that zanamivir is cleared slowly from the respiratory     tract. Antimicrob. Agents and Chemother. 43, 11, 2642-2647. 

1-27. (canceled)
 28. A method for the prevention of an orthomyxovirus or paramyxovirus infection, comprising the step of administration to a subject in need thereof of an effective amount of a compound of formula (I)

in which R is an amino or guanidino group; R² is acetyl or trifluoroacetyl; and n is an integer from 10 to 14, or a pharmaceutically acceptable salt, ether, ester or salt of such ester thereof.
 29. A method according to claim 28 in which the orthomyxovirus or paramyxovirus infection is an influenza A or B infection, parainfluenza, mumps or Newcastle disease.
 30. A method according to claim 28 in which the administration is to the respiratory tract by inhalation, insufflation or intranasally or a combination thereof.
 31. A method according to claim 28, further comprising the step of administering an effective amount of one or more anti-viral agents used to treat respiratory infections. 